The tool accepts an HTML file and two CSS files: the original before your code transformation
and the result of the transformation.

Then it uses PhantomJS and SlimerJS to load the HTML file twice:
once inlining the "before" CSS and once with the "after" CSS. The CSS is inlined in a <style> tag.

The HTML is stripped of tags such as iframe and script that can potentially skew the visual comparison
by injecting dynamic content.

The results of rendering the two HTML files are saved to two PNGs which are then compared pixel by pixel.

If they are different, a GIF animation is also created to help debug.

Finally, the "before" and "after" CSS files are copied, prettified, comment-stripped and sent to your
favorite diffing app so you can easily see what changed in the CSS. The prettification is done with the
Mensch CSS parser/stringifier